This invention relates to improvements in a semiconductor device including a collector, an emitter and a base region in a semiconductor substrate.
In order to increase the withstanding voltage of bipolar transistors and improve the high frequency characteristics thereof, there have been already proposed gate associated transistors comprising a first collector region highly doped, for example, with an n type impurity, a second n.sup.- type collector region disposed on the first n.sup.+ type collector region, a p type base region disposed in the second n.sup.- type collector region, an n.sup.+ type emitter region disposed in the p type base region, and an annular p.sup.+ type gate region extending from the p type base region in the second n.sup.- type collector region to encircle a current path along which the principal current flows between the emitter region and the collector regions. In such transistors it has been possible to increase the impurity concentration of the collector regions to increase the maximum usable current and also decrease the voltage drop at that current. However, this increase in impurity concentration has reduced the spread of a depletion layer in the n.sup.- type collector region resulting in a decrease in the withstanding voltage. That is, an increase in withstanding voltage has heretofore been incompatible with both an increase in maximum usable current and a decrease in voltage drop.
Accordingly it is an object of the present invention to provide a new and improved semiconductor device having a high withstanding voltage, and good high frequency characteristics while having a low power loss during operation.
It is another object of the present invention to provide a new and improved semiconductor device having a high withstanding voltage, good high frequency characteristics a high current capacity and a high output.